Three dimensional conductive strap for a magnetorestrictive sensor.

ABSTRACT

A magnetoresistive sensor has a semiconductor substrate and an insulator over the substrate. A magnetoresistive film is embedded in the insulator responsive material, and a conductive strap is wound into a coil around the magnetoresistive film but not around the substrate.

RELATED APPLICATION

[0001] U.S. patent application Ser. No. (B10-16122) discloses subjectmatter which is similar to the subject matter disclosed herein.

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention relates in general to magnetic fieldsensors and, more particularly, to magnetoresistive sensors.

BACKGROUND OF THE INVENTION

[0003] Magnetoresistive sensors are typically small, and generallymeasure magnetic fields on the order of 0.001 gauss to 100 gauss. Also,magnetoresistive sensors are able to measure D.C. fields as well asfields having frequencies up to and exceeding one megahertz.Accordingly, magnetoresistive sensors are used in a wide variety ofapplications such as current sensing, proximity sensing, etc.

[0004] The magnetoresistive material used in making magnetoresistivesensors is a material whose resistance changes in the presence of amagnetic field. Permalloy, which is a nickle/iron alloy, is such amaterial and is often provided as a film in a layer above an integratedcircuit wafer. The resistance of the film varies according to the squareof the cosine of the angle between the magnetization direction of thefilm and the direction of the current running along the length of thefilm. When the magnetization of the film is parallel to the current, theresistance of the film is at a maximum. On the other hand, when themagnetization of the film is perpendicular to the current, theresistance of the film is at a minimum.

[0005] The response of a magnetoresistive material is measured asΔR/R_(N), where ΔR is the change in resistance of the magnetoresistivematerial and R_(N) is the nominal resistance of the magnetoresistivematerial. The change in the resistance ΔR of Permalloy between the pointwhere the magnetization direction is parallel to the current directionand the point where the magnetization direction is perpendicular to thecurrent direction is typically on the order of 2% of the nominalresistance of the material.

[0006] Moreover, the plot of ΔR/R_(N) versus the angle between themagnetization direction and the current direction is bell shaped. Inorder to operate the magnetoresistive material on the linear part ofthis curve, a bias field is frequently applied to the magnetoresistivesensor. For example, either a solenoid wrapped around themagnetoresistive sensor package or a plurality of thin-film permanentmagnets at the end of the magnetoresistive sensor are usually used toapply an external biasing field so as to bias the magnetoresistivematerial at this linear portion.

[0007] Alternatively, instead of applying an external biasing field, itis known to apply an internal biasing field to the magnetoresistivesensor. Accordingly, the magnetoresistive sensor is provided with aconductive strap, which is usually referred to as a set/reset strap. Aset-reset strap is fabricated using known integrated circuit processingtechniques to form a serpentine conductor typically in a layer above themagnetoresistive film. A current may be applied in either directionthrough the set/reset strap so as to selectively bias the magnetizationdirection of the magnetoresistive film.

[0008] This set/reset strap may also be used as an offset strap toeliminate the offset due to mismatched magnetoresistive bridge elementsand due to temperature differences between magnetoresistive films whenseveral magnetoresistive films are arranged in a bridge configuration ina single sensor structure. The offset strap can also be used toeliminate offset drift in the bridge measurement electronics.

[0009] As indicated above, known set, reset, and/or offset strapsmeander in a single plane or layer of a magnetic device such as amagnetoresistive sensor. Accordingly, when multiple magnetic devices areformed on a semiconductor wafer, a substantial amount of the wafer realestate is used to form the strap, which imposes a restriction on thenumber of magnetic devices that can be formed on the wafer. Moreover,known set, reset, and/or offset straps which meander in a single planeor layer of a wafer require a relatively large current flow to producethe required magnetic field.

[0010] The present invention is directed, at least in one embodiment, toa strap which overcomes one or more of the problems noted above.

SUMMARY OF THE INVENTION

[0011] In accordance with one aspect of the present invention, amagnetic sensor comprises a semiconductor substrate, a magneticallyresponsive material formed above the semiconductive substrate, and aconductive strap wound into a coil around the magnetically responsivematerial such that at least a portion of the conductive strap is betweenthe magnetically responsive material and the substrate.

[0012] In accordance with another aspect of the present invention, amagnetoresistive sensor comprises a semiconductor substrate, aninsulator over the substrate, a magnetoresistive film embedded in theinsulator responsive material, and a conductive strap wound through theinsulator so as to form a coil around the magnetoresistive film.

[0013] In accordance with yet another aspect of the present invention, amagnetoresistive sensor comprises a semiconductor substrate, amagnetoresistive material, and a three-dimensional conductive strap. Themagnetoresistive material is formed above the semiconductive substrate.The three-dimensional conductive strap is formed above thesemiconductive substrate, and has a position with respect to themagnetoresistive material so as to set the magnetization direction ofthe magnetoresistive material when the three-dimensional conductivestrap is supplied with current.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other features and advantages will become more apparentfrom a detailed consideration of the invention when taken in conjunctionwith the drawing in which:

[0015]FIG. 1 is a cross-sectional side view of a magnetoresistive sensoraccording to an exemplary embodiment of the present invention; and, FIG.2 is a top view of the magnetoresistive sensor of FIG. 1.

DETAILED DESCRIPTION

[0016] As shown in FIGS. 1 and 2, a magnetoresistive sensor 10 includesfirst and second insulators 12 and 14 formed over a substrate 16. Forexample, the material of the first and second insulators 12 may besilicon dioxide or a thermal oxide, and the substrate 16 may be silicon.

[0017] A magnetoresistive film 18 is embedded in the second insulator.Because the view of FIG. 1 is an end view, the length of themagnetoresistive film 18 goes into the page as the reader observesFIG. 1. The resistance of the magnetoresistive film 18 is dependent uponthe magnetic field to which the magnetoresistive sensor 10 is exposed.Permalloy or other magnetoresistive material may be used for themagnetoresistive film 18. For example, the magnetoresistive film 18 mayhave a thickness of 175 Å, and a length to width ratio of 16/1. However,it should be understood that these dimensions are exemplary only andthat they are application dependent. Different dimensions may be useddepending on the required sensitivity of the magnetoresistive sensor 10.

[0018] A conductive strap 20 is formed into a coil 22 around themagnetoresistive film 18. As viewed in FIG. 1, the turns of the coil 22travel into the page as they spiral around the magnetoresistive film 18.Copper, aluminum, a copper/aluminum alloy, or other non-magneticconductive material may be used for the conductive strap 20. Forexample, the conductive strap 20 may have a thickness of 2 microns, anda width of 20 microns, and a length sufficient to form a coil around themagnetoresistive film 18. However, it should be understood again thatthese dimensions are exemplary only and that they are applicationdependent. The first and second insulators 12 and 14 should have athickness sufficient to electrically insulate the magnetoresistive film18 and the conductive strap 20 from each other and from the substrate16.

[0019] The first turn of the coil 22 begins with a first segment 24 ofthe conductive strap 20 that passes through the second insulator 14 tocontact a second segment 26 of the conductive strap 20. The secondsegment 26 of the conductive strap 20 is buried between the first andsecond insulators 12 and 14, traverses the width of the magnetoresistivefilm 18, and contacts a third segment 28 of the conductive strap 20. Thethird segment 28 of the conductive strap 20 passes through the secondinsulator 14 to contact the second segment 26, and also travels alongthe surface of the second insulator 14 to complete the first turn of thecoil 22.

[0020] A second turn of the coil 22 begins with a fourth segment 30 ofthe conductive strap 20 that contacts the end of the third segment 28 ofthe conductive strap 20 but does not contact the first and secondsegments 24 and 26 of the conductive strap 20. The fourth segment 30 ofthe conductive strap 20 passes through the second insulator 14 tocontact a fifth segment 32 of the conductive strap 20. The fifth segment32 of the conductive strap 20 is buried between the first and secondinsulators 12 and 14, traverses the width of the magnetoresistive film18 behind the second segment 26 of the conductive strap 20, and contactsa sixth segment 34 of the conductive strap 20 which is behind the thirdsegment 28 of the conductive strap 20. The sixth segment 34 of theconductive strap 20 passes through the second insulator 14 to contactthe fifth segment 32, and also travels along the surface of the secondinsulator 14 behind the third segment 28 to complete the second turn ofthe coil 22. Accordingly, none of the segments of the second turn of thecoil 22 contact any of the segments of the first turn of the coil 22,except that the end of the third segment 28 contacts the beginning ofthe fourth segment 30.

[0021] Any remaining turns of the coil 22 are similarly formed.

[0022] Because the conductive strap 20 is wound into the coil 22 aroundthe magnetoresistive film 18 in all three dimensions (x, y, and z), theresulting magnetoresistive sensor is smaller than when a known singleplane or layer set/reset and offset strap is used. Accordingly, whenmultiple magnetic devices are formed on a semiconductor wafer, theconductive strap 20 of the present invention permits more magneticdevices to be formed on a wafer than do known set/reset and offsetstraps. Thus, the conductive strap 20 of the present invention reducesfabrication costs.

[0023] Moreover, the coil 22 formed by the three dimensional winding ofthe conductive strap 20 produces about twice as much magnetic field forthe same current as do known set/reset and offset straps that meander ina single plane or layer of a wafer. Alternatively, the coil 22 formed bythe three dimensional winding of the conductive strap 20 produces aboutthe same magnetic field at half the current as do known set/reset andoffset straps that meander in a single plane or layer of a wafer. Theuse of less current produces less thermal stress on the conductive strap20.

[0024] As shown in FIG. 2, dimension A=20 microns, dimension B=15microns, dimension C=20 microns, and dimension D=20-40 microns dependingon number of turns. However, it should be understood yet again thatthese dimensions are exemplary only and that they are applicationdependent.

[0025] Certain modifications of the present invention will occur tothose practicing in the art of the present invention. For example, thepresent invention has been described above in terms of amagnetoresistive sensor. However, the present invention may be used withother types of magnetic sensors.

[0026] Accordingly, the description of the present invention is to beconstrued as illustrative only and is for the purpose of teaching thoseskilled in the art the best mode of carrying out the invention. Thedetails may be varied substantially without departing from the spirit ofthe invention, and the exclusive use of all modifications which arewithin the scope of the appended claims is reserved.

What is claimed is:
 1. A magnetic sensor comprising: a semiconductorsubstrate; a magnetically responsive material formed above thesemiconductive substrate; and, a conductive strap wound into a coilaround the magnetically responsive material such that at least a portionof the conductive strap is between the magnetically responsive materialand the substrate.
 2. The magnetic sensor of claim 1 wherein theconductive strap comprises a plurality of segments forming the coil. 3.The magnetic sensor of claim 2 wherein the segments consist ofhorizontal and vertical segments.
 4. The magnetic sensor of claim 1wherein the conductive strap comprises a non-magnetic conductivematerial.
 5. The magnetic sensor of claim 1 wherein the conductive strapcomprises copper.
 6. The magnetic sensor of claim 1 wherein theconductive strap comprises aluminum.
 7. The magnetic sensor of claim 1wherein the conductive strap comprises a copper/aluminum alloy.
 8. Themagnetic sensor of claim 1 further comprising an insulator, wherein themagnetically responsive material is embedded in the insulator.
 9. Themagnetic sensor of claim 8 wherein the conductive strap comprises aplurality of vertical and horizontal segments forming the coil.
 10. Themagnetic sensor of claim 8 wherein the conductive strap comprises anon-magnetic conductive material.
 11. The magnetic sensor of claim 8wherein the insulator comprises silicon dioxide.
 12. A magnetoresistivesensor comprising: a semiconductor substrate; an insulator over thesubstrate; a magnetoresistive film embedded in the insulator responsivematerial; and, a conductive strap wound through the insulator so as toform a coil around the magnetoresistive film.
 13. The magnetoresistivesensor of claim 12 wherein the conductive strap comprises a plurality ofsegments deployed in at least two layers to form the coil.
 14. Themagnetoresistive sensor of claim 13 wherein the segments comprisesubstantially linear, elongated portions.
 15. The magnetoresistivesensor of claim 12 wherein the conductive strap comprises a non-magneticconductive material.
 16. The magnetoresistive sensor of claim 12 whereinthe insulator comprises silicon dioxide.
 17. A magnetoresistive sensorcomprising: a semiconductor substrate; a magnetoresistive materialformed above the semiconductive substrate; and, a three-dimensionalconductive strap formed above the semiconductive substrate, wherein thethree-dimensional conductive strap has a position with respect to themagnetoresistive material so as to set the magnetization direction ofthe magnetoresistive material when the three-dimensional conductivestrap is supplied with current.
 18. The magnetoresistive sensor of claim17 wherein the conductive strap comprises a plurality of segments inmultiple layers so as to form a coil around the magnetoresistivematerial.
 19. The magnetoresistive sensor of claim 18 wherein thesegments comprise substantially linear, elongated portions.
 20. Themagnetoresistive sensor of claim 17 wherein the conductive strapcomprises a non-magnetic conductive material.
 21. The magnetoresistivesensor of claim 20 wherein the non-magnetic conductive materialcomprises copper.
 22. The magnetoresistive sensor of claim 20 whereinthe non-magnetic conductive material comprises aluminum.
 23. Themagnetoresistive sensor of claim 20 wherein the non-magnetic conductivematerial comprises a copper/aluminum alloy.
 24. The magnetoresistivesensor of claim 17 further comprises an insulator, wherein themagnetoresistive material is embedded in the insulator.
 25. Themagnetoresistive sensor of claim 17 wherein the conductive strapcomprises a plurality of turns forming a coil around themagnetoresistive material but not around the substrate.
 26. Themagnetoresistive sensor of claim 25 wherein the conductive strapcomprises a non-magnetic conductive material.